Sewage screening system



Sept. 26, 1944.

J. D. WALKER SEWAGE SCREENING SYSTEM Filed March 4, 1940 2 Sheets-Sheet l Sept. 1944' J. o. WALKER 2,358,841

SEWAGE SCREENING SYSTEM Filed March 4, 1940 2 Sheets-Sheet 2 INVENT OR.

Ja/7w5fl WWW BY W ATTORNEYS.

Patented Sept. 26, 1944 SEWAGE SCREENING SYSTEM James D. Walker, Aurora, Ill., asslgnor to The American Well Works, Aurora, IlL, a corpora-- tion of Illinois Application March 4, 1940, Serial No. 322,073

9 Claims.

in sewage disposal plants it is common practice to provide screens for initially screening out objects which will not go through the plant satisfactorily, For example, fibrous r rubbery objects are likely to jam the pumps. Unless special pumps are used, many of these objects will not dissolve. These same insoluble objects, however, are likely to clog the screens which are provided for removing them. Accordlingly, it is a practice to clean these screens at fairly frequent intervals with a hand rake or the like. Although machinery has been provided for cleaning the screens mechanically, it is very expensive and is likely to be troublesome and undependable.

According to the present invention a simple system is provided in which the screens are automatically cleaned periodically by means of causing a backwash of the sewage liquors which wash the insoluble particles from the screen. They are preferably simultaneously drawn into a pump which serves to cut them up and pass them into the sewage in an unobjectionable form. v

Additional objects and advantages of the invention will be apparent from the following description and from the drawings, in which:

Fig. 1 is a plan view of the apparatus chosen for illustration of this invention.

Fig. 2 is a vertical longitudinal sectional view therethrough taken approximately on the line 2-2 of Fig. 1 and showing the circuit connection diagrammatically.

Fig. 3 is a view corresponding to Fig. 2, showing the screens being flushed while Fig. 2 shows them partly obstructed.

Fig. 4 is a transverse sectional view taken approximately on the line 4-4 of Fig. 2.

A preferred form of the invention has been chosen for illustration and description, in compliance with section 4888 of the Revised Statutes, but persons skilled in the art will readily perceive other means utilizing the inventive concepts covered by the claims for accomplishing the sam results.

The invention has been illustrated in connection with a screening tank ll into which the sewage flows through a pipe I2. The tank may include a plurality of screens l3 and I4 positioned between the inlet l2 and an outlet IS. The outlet l6 may be positioned at a height to maintain the liquor at the desired level, or preferably a wall I! will be provided for this purpose. The sewage will normally flow into the tank through the pipe l2, through the screens l3 and [4 which will remove foreign objects therefrom, and then over the wall I! to the outlet it. As

seen from Fig. 1, two screens I3 lie in vertical planes and are inclined toward a pump inlet l9. As seen from Fig. 2, the top screen I4 is inclined downwardly and toward the pump inlet l9. The inlet l9 communicates with a comminuting pumpv 2| which is preferably of the type disclosed in the application of Knute Hartman, Serial No. 256,117; now Patent No. 2,245,035, issued June 10, 1941. This pump has the advantage that it will out foreign objects into small bits so that they may pass through the sewage plant with the sewage without causing any trouble. When it is used to pumpall of the sewage, it is not essential to screen the sewage, but in that event'the pump must be run continuously. According to the present invention the screens I3 and I are used so that ordinarily the sewage may flow through them by gravity and the pump 2| is used only periodically to flush out the screens I 3 and I4, incidentally comminuting the insoluble objects.

As sewage flows through the screens l3 and H the solid objects will catch on the bars of the screen. Ithas long been the practice to use parallel bars without cross bars so as to minimize this effect and to facilitate cleaning. However, the particles will catch nevertheless and frequent cleaning has always been necessary.

According to the present invention this cleaning is accomplished by periodically starting a motor 23 which drives the pump 2|. This drawsthe liquor rapidly from the inlet side of screens l3 and i4 and expels it on the outlet side thereof through outlet 24. This lowers the liquor level on the inlet side and may slightly raise it on the outlet side. In thus lowering the level in advance of the screens it causes a backfiow of liquor through the screens, as suggested by Fig. 3, and this backflow cleans the foreign objects from the screens. they are drawn with the liquor into the pump 2| and are cut up by the pump and discharged in harmless bits into the sewage.

. Although it is very desirable to use a comminuting pump 2| so as to cut the objects into small enough pieces so that they will be unobjectionable, this is not necessary for the purpose of cleaning the screens. In fact, it is evident that anything that suddenly lowers the level of the liquor in advance of the screens so that backfiushing occurs would accomplish the same results in so far as cleaning the screens is concerned.

Although the side screens 13 would ordinarily provide sufllcient flow area, provision of the additional screen l4 serves as a safeguard against When thus washed from the screens,

-nectecl in parallel with the time switch and the flow of unscreened sewage if the screens II should become so obstructed as to cause a substantial rise in the liquor level. Heretofore when screens have been positioned so that the bars thereof extend from below the liquor-level to above the liquor level, a mass of foreign objects have accumulated on the screen above the liquor level. It is apparent that if this were the case in the present instance the backwash would be below the level of these foreign objects and hence they would not be washed off. This trouble is avoided by inclining the screen downwardly in the direction of flow of the sewage instead of upwardly in the direction of flow as heretofore. Heretofore the movement of the sewage has washed the foreign objects upwardly along the screen bars, whereas according to the present invention it washes them downwardly along the screen bars, being aided in this by gravity. Many of these foreign objects will be washed to the ends of bars of screen l3 and then will drop of! the bars and settle adjacent to the intake nozzle I! of the pump. This is not necessary, however,

since they will at least be washed far enough along the bars of screens ll so that the backwash will remove them from the screens so that they can be drawn into the nomle i3. The spaces between the screens l3 and I are of course obstructed, as by plates 2!. These plates may each conveniently have one wall, as seen in Fig. 2, in alignment with a screen l3, and the other wall, seen in Fig. 1, in alignment with the screen it. The two walls may be formed from a single plate or by separate plates joined together.

The path through the pump 2| is sufllciently tortuous and narrow so that, unless the pump is operated, there will be little or no flow through it. Flow through it between operations could be prevented by positioning its outlet above the highest level of the sewage in advance of the screens. It may be noted, incidentally, that the outlet 24 may open in any direction. It is preferred not to have it directed onto the screen ll, however, because if it is directed in some other direction there will be a larger proportion of screened sewage flowing back through the screens in backwashing. On the other hand, if any difficulty were encountered in cleaning a particular screen i, the outlet 24 could be directed thereon to clean the screen more thoroughly.

In Fig. 2 the circuit for the motor 23 has been diagrammatically indicated. From a suitable source of power, not shown, one lead 26 may go directly to the motor while the other lead 21 may be connected to the source of power through a suitable time switch 28. This time switch will turn on the motor 23 as frequently as may be found necessary and for such periods as may be found necessary. Five minutes in every two or three hours is believed to be adequate, although individual operators may prefer more frequent backflushing of the screens. With as long a period as this it may be desirable to provide a hand switch 29 so that if the attendant notices that the screens are becoming clogged in a shorter interval, he can operate the motor by hand. Of course, a hand switch would usually. be provided in any event, simply to take care of emergency. Likewise, a normally closed hand switch 3| will be provided for preventing operation of the motor 23 when this section of the plant is shut down.

As an added safeguard or in place of the time switch 28 it may be desirable to provide a floatcontrolled switch 22. This switch will be conmanual switch 28 and will operate to close the circuit and run the motor 23 whenever the liquor level in advance of the screens l3 and I4 is above a predetermined point. Thus, if the screens l3 and I4 should become so obstructed as to create a dangerous or objectionable condition, the level of the liquor in advance of the screen would rise. In rising it would raise a float 33 which may be protected by a shield 34. This float carries a rod 35 which slides through a. hole in operating arm 36 of switch 32. Collars 31 are adjustably positioned on rod 35. When the liquor level rises to a predetermined point, the lower collar 31 will raise the arm 36 and turn on the switch 32. The pump would then start and pump the sewage from the inlet side of the screens l3 and I4 until the liquor level on the inlet side of the screens has been lowered enough for the upper collar 31 to shift the arm 36 to the off" position, the switch 32 of course being a snap type switch. By positioning the upper collar 31 able.

to permit the liquor level to be lowered nearly as low as possible, backflushing will be obtained and the screens will be adequately cleaned.

In view of the foregoing description, a brief explanation of the operation will be sufficient. Sewage flows in through the inlet I2 and normally flows through the screens l3 and I, over the wall I1 and out the outlet l8. Objectionable foreign objects will be caught on the screens l3 and I4. Periodically, either by operation of the time switch 28, the manual switch 29, or the float-controlled switch 32, motor 23 will be started and it will drive the impeller in the pump 2|.

This will draw liquor into the intake I9 sufllciently rapidly to lower the level of the sewage in advance of (on the inlet side of) screens l3 and H until it is lower than the top of the wall H. The sewage beyond the screens |3 and I4 will then backwash through the screens l3 and I4, thus flushing from them the foreign objects which have been caught thereon. These foreign objects will be drawn into the pump 2| with the sewage flowing through the pump inlet l9 and will be comminuted by this pump into pieces too small to cause trouble or to be objectionable. After a time interval sufllcient to thoroughly clean the screens l3 and H the motor 23 and pump 2| will be stopped by operation of the time switch 28, manual switch 29, or float controlled switch 32. If both the time switch 28 and float controlled switch 32 are provided, only the time switch will ordinarily operate, the float controlled switch operating only in the event of exceptional conditions causing obstruction of the screen and a severe rise of the liquor within the normal idle period of the motor 23 and pump 2|.

From the foregoing it is seen that a sewage screening system has been provided in which the screens are automatically cleaned by backilushing and the objects flushed therefrom are comminuted so as to be rendered harmless and unobjection- The system permits gravitational flow of the sewage normally, the pump being used only for a short time at rare intervals to flush the screens. It is evident, therefore, that the power consumed by the pump is negligible, although all of the foreign objects which do not pass through the screens are comminuted by the pump. With an operating cost less than that required for keeping screens cleaned heretofore, the screens are cleaned and in additionthe foreign objects caught thereby are cut up into small harmless pieces.

Even without the backwash, the pump 2| would do a good job of cleaning the screens since the flow of water along the screens into intake nozzle i8 would wash the screenings into the nozzle l9, particularly in view of the fact that the spaces between the screen bars are unobstructed at their ends, the support members being secured to these screen bars along their rear sides. Likewise, if a portion of the sewage, or all of the sewage periodically, were allowed to flow through a conduit in the place of the pump intake l9, the screenings would gradually be washed along the bars and off of them at their ends. Thus, they could be diverted permanently from the main stream or comminuted other than by the pump 2| and returned to the sewage leaving the outlet it.

I claim:

1. Screening apparatus for sewage and analogous liquors, including a generally horizontal conduit, a screen across said conduit, means for maintaining a normal level of liquor flowing generally horizontally through the screen, a pump having an intake communicating with the upstream side of the screen for drawing liquor of! .without its passing through the screen to lower the liquor level on the upstream side of the screen so that liquor which has already passed through the screen will flow back through the screen again, flushing from the screen objects which have been caught thereon, a time switch for automatically causing the occasional operation of said pump, and an independently effective switch responsive to the level of the liquor on the upstream side of the screen for causing the operation of the pump.

2. Screening apparatus for use in a system for treating sewage and analogous liquors, including a screen, means for maintaining a normal level of liquor flowing through the screen, a pump having an intake communicating with the upstream side of the screen for occasionally drawing liquor off without its passing through the screen to lower the liquor level on the upstream side of the screen so that liquor which has already passed through the screen will flow back through the screen again, flushing from the screen objects which have been caught thereon, said pump including cutting means to cut the objects into small bits which may pass through the sewage system without causing trouble, discharge means for delivering the cut up objects and liquor back into the system from the pump, and means for controlling the pump to cause it to operate for only a short period at infrequent intervals;

3. Screening apparatus for sewag and analogous liquors, including a generally horizontal conduit, a screen across said conduit, means for maintaining a normal level of liquor flowing generally horizontally through the screen, mean having an intake communicating with the upstream side of the screen for drawing liquor off without its passing through the screen to lower the liquor level on the upstream side of the screen so that liquor which has already passed through the screen will flow back through the screen again flushing from the screen objects which have been caught thereon, and means for controlling the operation of said liquor draw-off means automatically at predetermined intervals of time and in response to a predetermined rise of the liquor level-on the upstream side of the screen.

4. Screening apparatus for use in a system for treating sewage and analogous liquors, including a generally horizontal conduit, a screen across said conduit, means for maintaining a normal level of liquor flowing generally horizontally through the screen, and a pump having an intake communicating with the upstream side of the screen for occasionally drawing liquor oil without its passing through the screen to lower the liquor level on the upstream side of the screen and having an outlet for discharging the liquor back into the system so that liquor which has already passed through the screen will flow back through the screen again, flushing from the screen objects which have been caught thereon, the screen sloping toward the inlet to the pump whereby the normal movement of the liquor through the screen tend to move the foreign objects to the pump inlet; said pump inlet being constantly open.

5. Sewage screening apparatus for use in a sewage treating system, including a screen, an infiuent conduit normally open to the screen, an eilluent conduit from the other side of the screen disposed for horizontal flow of the sewage through the screen and so constructed and arranged as to form a reservoir of substantial volume adjacent the screen, an outlet for the eiiluent conduit, and a' pump having an intake on the influent side of the screen and near the bottom of the screen an outlet discharging back into the system, and having suflicient pumping capacity to cause a substantial stream to flow from the reservoir backwards through the screen and into the pump, whereby substantially all of the solids caught by said screen can be washed into the pump while maintaining a pool of liquor above the pump intake; said apparatus including means for so treating the sewage drawn into the intake that the liquor discharged through its outlet will be substantially free from large screenings.

6. Sewage screening apparatus including a screen, an influent conduit normally open to the front of the screen with the screen disposed thereacross, an eiiluent conduit from the rear of the screen disposed for horizontal flow of the sewage through the screen, and cutting and recirculating means including a pump having an outlet at the rear of the screen, so positioned that a substantial portion of the liquor discharged therefrom can pass through the screen from rear to front, and an intake at the front of the screen and near the bottom of the screen, and having suflicient pumping capacity to cause a substantial stream to flow and recirculate backwards through the screen and through the pump while the influent conduit is open, whereby substantially all of the solids caught by said screen can be washed into the pump while maintaining a pool of liquor above the pump intake; said apparatus including means for so treating the sewage drawn into the intake that the liquor discharged through its outlet will be substantially free from large screenings.

7. Sewage screening apparatus including a screen, an influent conduit at the front of the screen, an eiiluent conduit from the rear of the screen, and recirculating means including a pump having an outlet at the rear of the screen, so positioned that a substantial portion of the liquor discharged therefrom can pass through the screen from rear to front, and an intake at the front of the screen and near the bottom of the screen, and having suflicient pumping capacity to cause a ubstantial stream to flow and recirculate backwards through the screen and through the pump whereby substantially all of the solids caught by said screen can be washed into the pump while maintaining a pool of liquor above the pump intake; said apparatus including cutting means associated with said recirculating means for cutting up any large solids drawn into said intake.

8. Sewage screening apparatus including a conduit through which sewage flows substantially horizontally, a screen across said conduit, 9. pump having an intake on the upstream side of the screen and adjacent the screen, and adapted to draw liquor and screenings entrained in said liquor from the main stream through the screen and having an outlet adapted to discharge said liquor and screenings back into the main stream. said apparatus including means for cutting. up any large solids drawn into said intake before they are discharged back into the stream, and automatic control means for operating the pump and cutting means only infrequently whereby only a very small portion of the liquor in the main stream flows through said pump.

9. Sewage screening apparatus including a conduit through which sewage flows substantially horizontally, a screen across said conduit, a pump having an intake on the upstream side of the screen and adjacent the screen, and adapted to draw liquor and screenings entrained in said liquor from the main stream through the screen and having an outlet adapted to discharge said liquor and screenings back into the main stream, said apparatus including means for cutting up any large solids drawn into said intake before they are discharged back into the stream.

JAMES D. WALKER. 

